The rear hitch of an agricultural tractor is arranged to engage with various attachment mechanisms associated with implements and trailers. There are two main mechanisms by which an implement can be attached to a tractor. Some implements are mounted to a three-point linkage wherein the tractor rear hitch includes a pair of lower lift arms and a top link which all attach to the implement forming a triangulation structure. This allows implements such as ploughs, hay tedders and hedge cutters to be lifted from the ground by appropriate control of the lower linkage arms thus transferring all weight from the implement to the tractor.
Other implements such as trailers, rollers and balers are attached to a drawbar for hauling. This group of implements either comprises its own axle (trailers and balers) or is required to transfer weight to the ground to function (rollers).
Known agricultural tractor rear hitches permit a drawbar to be removed from the rear hitch or adjusted wherein the rearward extension of the drawbar can be changed to cater for various tasks. Many rear hitch designs also cater for a variety of implement connector plates which are interchangeable to cater for various towed implements. For example, one implement connector plate may include a ball coupling whereas another may include a piton coupling.
As agricultural tractor technology advances so too does the maximum speed at which tractors are permitted to travel on highways. This carries the burden of various regulation requirements such as the need to upgrade braking systems on the vehicle.
In attempting to improve braking systems, it has proved desirable to vary the braking force depending upon load. In particular, a braking force of a tractor and trailer combination can be spread across the axles of the tractor and trailer depending upon the load on the trailer. For example, a vehicle towing a heavy load will apply a greater braking force to axles upon the towed vehicle thus saving wear on the brakes of the towing vehicle and reducing the risk of jack-knifing.
Various attempts have been made to provide means to measure the load placed by an implement on a drawbar. For example, International patent application number WO-91/02226 discloses a force measurement device for a trailer coupling which measures the vertical force component acting upon the coupling between a towing vehicle and a towed vehicle.